I figured l would post an update. The local boat repair shop had all of the parts to do the conversion in stock so I went for it. I went ahead and sprang for a new set of champion plugs since if my too-much-oil theory was correct the current ones would be badly fouled.
It only took about two...
Motor is a 1992 40hp, J40TLENM. Man, where to start. The last time I had it running on the water was in 2023. It had the idle issue then but I "lived with it." This year I decided to try and get past it so I just put in Sierra carb kits, and did everything down to pulling and replacing the lead...